Earlier studies, utilizing irradiation as the mutagenic source, have shown that the genome of the test organism is a major factor in the determination of its susceptibility to genetic damage. It is our purpose to investigate to what extent such genetically caused differences in sensitivity pertain to other mutagenic agents. We also want to know if the relative level of sensitivity of a defined genome to induction of mutations is constant for all agents or variable depending on the mutagen used. Preliminary screening of five inbred strains using chemical mutagens indicates the existence of strain differences among these strains of mice. Future efforts will include retests of these strains plus tests of additional strains. In addition, efforts will be devoted to understanding the underlying genetic causes of the differences.